A walk behind lawn mower is typically provided with a pair of rear wheels that can be selectively powered by pivoting a drive lever consisting of a half loop lever provided on a handlebar of the mower toward the cross member of the handlebar. A drive clutch is provided between the engine of the mower and the rear wheels, and the drive lever enables the operator to selectively disconnect the transmission path between the engine and the rear wheels by means of the drive clutch.
The dog clutch is known in the art, and has the advantage of being compact and simple in structure. U.S. Pat. No. 7,669,702 discloses the use of a pair of dog clutches to accommodate the difference in the rotational speed between the two rear wheels during the cornering of the mower.
During the normal mowing operation, the driven rear wheels are highly effective in reducing the effort required by the operator. However, when mowing the grass on a slope, the operator may desire to selectively power the rear wheels. More specifically, whereas it is desirable to power the rear wheels when mowing uphill, it is desirable to disconnect the power when mowing downhill. When mowing the grass on a slope, the operator typically stands under the slope, and pushes the mower uphill using the power of the engine and pulls back the mower downhill using the gravitational force with the power to the rear wheels disconnected. Pushing and pulling the mower back and forth also occur in other situations such as when mowing grass in spatially tight areas and areas adjoining fences and other obstacles.
More recently, electrically powered mowers that offer the advantages of lower emission levels and lower noise levels have been introduced. The cutter blade may be powered either by an internal combustion engine or an electric motor, but it is particularly advantageous to use an electric motor to power the driven wheels of the mower owing to the advantage of simplifying the transmission system for transmitting the power of the power source to the driven wheels. The inventors of this application have also noted a new possibility in an increased freedom in controlling the power that can be transmitted from the electric motor to the driven wheels.